1. Field of the Invention
This invention provides a novel package for RF transistors which offers improved stability to wave and vapor phase soldering.
2. Description of Related Art
Hybrid RF power, semiconductive devices, or packages, are well-known in the art. Typically such devices or packages include a transistor and an input capacitor mounted upon appropriately metallized surfaces of a beryllia substrate including a lead frame arrangement bonded to the metallized areas which includes input, output and ground portions or members. Appropriate wire bonds extend from the active portions of the transistor and capacitor to the various lead portions as is well understood. Such hybrid devices, or packages, may be characterized as having an input circuit and output circuit and a common circuit which includes common lead inductance.
The beryllia substrate is electrically insulating but thermally conducting and is usually mounted upon a relatively massive metallic heat sink. Appropriate ground connections may be made to the grounded heat sink. Further, the input and output circuits usually comprise microstrip conductor means which include a metallic strip mounted on an insulating substrate whose impedance are matched to those of the input and output circuits of the transistor. In addition, the microstrip circuit devices may also be grounded to the metallic heat sink, for example, by wrap around metallizations.
The RF transistor packages have protective caps sealed over the active silicon device with epoxy. Automated package assembly techniques, such as wave soldering and vapor phase soldering, employ temperatures and conditions which often cause breakdown of the epoxy and leakage of the solder into the active region of the device. In addition, when soldering onto a gold lead, the solder and solder flux may leach and travel along the gold underneath the epoxy. Equipment manufacturers must therefore rely on hand soldering of devices into boards after automatically inserting and soldering all other components.
There remains a need, then, for an improved package which will permit total automation of the assembly process.